During World War One, the railways were run by the government, until 1921. Railways Act 1921 merged most of the minor lines, like the Cambrian Railways, into the four biggest firms, who took them over.[1] Complete nationalisation had been considered but was rejected until the Transport Act 1947. The Cambrian Railways joined the Great Western Railway (GWR). The Staines and West Drayton Railway had already been taken over by the GWR many years earlier.

The Welsh Highland Railway had been deemed unnecessary and too costly to run. It was closed in 1937. The Second World War had caused damage to all the railways. They had lost a large part of their trains, buildings and equipment.

The Transport Act 1947 took effect on 1 January 1923. By that date most of the mergers had taken place, some from the previous year. The Railway Magazine in its issue of February 1923 dubbed the new companies as "The Big Four of the New Railway Era".

A major railway survey in April 1961 was used in the writing of a government report on the future of the network. This report was called The Reshaping of British Railways. It was published by the BRB in March 1963 as ("the Beeching Axe").[6][7] A third of all passenger trains would be scrapped and more than 4,000 of the 7,000 stations would be closed.

InterCity (or, in the earliest days, the hyphenated Inter-City) was introduced by British Rail in 1966 as a brand-name for its long-haul express passenger services (see British Rail brand names for a full history).

Passenger levels fell steadily from the late 1950s to the late 1970s,[8] but experienced a sharp increase after the introduction of the high-speed Intercity 125 trains in the late 1970s and early 1980s.[9]

Before the sectorization of BR in 1982 the system was split into regions. Working around London, they were London Midland Region (Marylebone, Euston, St Pancras and Broad Street), Southern Region (Waterloo, Victoria, Chairing Cross, Holborn Viaduct, Cannon Street and London Bridge), Western Region (Paddington) and Eastern Region (King's Cross, Moorgate, Broad Street, Liverpool Street and Fenchurch Street). This was perceived to be a source of inefficiency, so sectorization made the regions into a single organisation covering all commuter services. At the same time InterCity took over express services and Regional Railways took over regional services. The group was originally called Provincial.

BR built 2537 steam locomotives from 1948 to 1960, some to pre-nationalisation designs and some to its own, new, standard designs. Eventually BR chose to end the use of steam trains in 1968.

The official report known as the "Modernisation Plan"[10] of December 1954 was intended to bring the railway system into the 20th century. The aim was to increase speed, reliability, safety and line capacity, by making the railways more attractive to passengers and freight operators. The important areas were:

Closure of small numbers of unnecessary lines, stations and goods depots.

Long-distance trains from Marylebone began to be cut back from 1958 after the line was given from BR Midland Western to the BR Midland Region. Then BR Midland Region thought it was an unnecessary rival of their Midland Main Line.[11] By 1960 there were no daytime trains running to destinations north of Nottingham and only a few still ran at night.[11] Many Express services were cut.[11] By 1963, local stopping services beyond Aylesbury were cut. In 1965 freight services were ended.[11] Between 1963 and 1966 only a few remaining long distance services stayed in use. A large part of the former Great Central Railway was closed as part of the 'Beeching axe'. This meant that Marylebone was now used only by local trains to Aylesbury and High Wycombe. After the 1960s, lack of investment meant the station itself became run down.

The British Rail Class 423 (or 4Vep) electrical multiple units were built by BR at York Works from 1967 to 1974. They feature manually opening doors next to every seating row and mostly found working outer suburban services in South London, and rural services in Kent and Sussex, up to replacement in 2005.

British Rail Class 313electric multiple units were built by BREL at York Works from 1976 to 1977, thus the first second-generation EMUs to be constructed for British Rail. They were capable of both drawing power via 25 kV AC overhead, or 750 V DC third-rail. They were the first units in Britain to have fully automatic couplers which allowed both physical coupling and also the connection of control electric and air supplies to be carried out without the driver's need to leave the cab. Their passenger seats were also an improvement on former types.

During the late 1950s, railways continued to worsen, and in 1959 the government acted, limiting the amount the BTC could spend on British Rail.

The government proposed that many services could be provided more cheaply by buses, and said that most abandoned rail services would have their places taken by bus services. Only main lines would be untouched. Many other minor lines would be cut back or scrapped.

A major part of the report proposed that British Rail electrify some major main lines and the use of containerised freight traffic instead of outdated and uneconomic wagon-load traffic. Some of these plans were eventually adopted, however, such as the creation of the Freightliner concept and further electrification of the West Coast Main Line from Crewe to Glasgow in 1974. Also the staffs' terms and conditions were improved over time.

Since the Beeching cuts of the 1960s, road traffic levels grew heavily in some areas. This has come close to gridlock. Furthermore, in recent years there have been record high levels of passengers on the railways. A modest number of the railway closures have therefore been reversed.

In addition a small but significant number of closed stations have reopened, and passenger services been restored on lines where they had been closed or removed. Many of these were in the urban metropolitan counties and towns where Passenger Transport Executives have a role in promoting local passenger rail use.

In the early 1980s there was a proposal to close Marylebone and divert British Rail services via High Wycombe into nearby Paddington. There was also a plan to extend the Metropolitan Line to Aylesbury, so London trains via Amersham would be sent to Baker Street. Marylebone station was to be converted into a bus and coach station. London Underground said the Metropolitan Line could not cope with any more trains and was full up. However these plans were deemed stupid and clumsy, and were quietly dropped.

The funding of BR was reduced so they created the cheaper Pacer trains. The British Rail Class 143 is a diesel multiple unit, part of the Pacer family of trains introduced between 1985 and 1986. They originally worked around North East England but were later transferred to Wales.[16] It was made out of bus parts put on to lorry chassis and train wheels. Earlier units proved to be unreliable, but later units were of a better design.

On 12 December 1988, three commuter trains crashed, just south-west of Clapham junction station, in London. 35 people died and more than 100 were injured.[17] British Rail's 30-year-old vintageMark 1 carriages were found out to be dangerous and the broken signalling equipment was fixed and improved.

Some English stations like Corby and Mansfield were reopened after privatisation. Yet more stations were reopened by British Rail in Scotland, England and Wales before privatisation when the railway was run properly.

Sometimes strikes happened among British Rail staff, over staff pay, safety, working hours and alike. There were several strikes in the late 1970s, but decreased after privatisation. There were also several other strikes in the late 1970s. Other firms like the UK's coal mines also struck at this time.